The present invention relates to an oil coating apparatus which is one of constituent parts of a fixing apparatus in an electrostatic copying machine, an electrophotographic printer, or the like. Particularly, it relates to an oil coating roller which is one of constituent parts of a fixing apparatus in an electrostatic copying machine, an electrophotographic printer, or the like (especially, for the purpose of color copying or multicolor printing).
In a fixing apparatus in an electrostatic copying machine or in an electrophotographic printer, an oil coating roller rotating while touching a fixing roll directly or indirectly is generally provided to apply a very small quantity of silicone oil onto the fixing roll continuously to thereby prevent recording paper from being stained with toner remaining on the fixing roll.
Various types of oil coating rollers have been already provided. There are oil coating rollers of the type in which a cylindrical molded product of a metal pipe or heat-resistant fibers having a large number of pores in its wall is used as an oil holding member for storing oil to be applied and in which an oil coating member layer of heat-resistant felt is provided on a surface of the cylindrical molded product. Of this type oil coating rollers, an oil coating roller using, as the oil holding member, a porous cylindrical molded product containing heat-resistant fibers bound to one another by a binder and having fine communicating voids free from the binder among the fibers and evenly distributed pores with a pore size of from 0.05 to 2 mm and a total void percentage of from 30 to 90% (JP-A-9-108601) has a merit that oil is applied stably in a long term because not only the oil holding member can hold a large quantity of silicone oil but also the oil holding member can discharge silicone oil stably in a long term even under a high-loading condition.
In the case where the oil coating roller is used in a fixing apparatus for a color copying machine or a color printer, the aforementioned merit is unchanged but there is a tendency that the quantity of coating of oil increases excessively for a while (up to hundreds of sheets or a thousand sheets as the number of sheets of recording paper fed to the fixing apparatus) after the start of use because silicone oil having a relatively low viscosity of from 50 to 1000 cSt must be used on the basis of the necessity of applying a large quantity of oil onto the fixing roll compared with the case where the oil coating roller is used for a monochrome copying machine or a monochrome printer. Further, for the same reason, the quantity of oil exuding during the stopping of the machine increases. There is still a problem that a larger quantity of silicone oil than the proper quantity is applied onto the fixing roll for a short time just after the restart of paper feeding.
Further, in the case where copying or printing is performed for sheets of plastic OHP paper, unevenness in depth of toner occurs in an fixed image easily because very slight unevenness in application of oil has a bad influence on the fixing of toner. Although the surface of a felt layer formed of a felt tape wound helically is apparently flat, there is a delicate level difference in each of abutting portions in end surfaces of the felt tape. The level difference extends helically. Accordingly, though the level difference is slight, the level difference becomes a cause of stripe-like unevenness in application of oil and becomes a cause of unevenness in depth of toner in the fixed image as well.
Besides the aforementioned oil coating roller, various oil coating rollers have been already proposed. For example, there is an oil coating roller in which a cylindrical molded product of a porous hollow metal pipe or heat-resistant fibers is used as the oil holding member for storing release oil to be applied and in which an oil coating quantity control layer of a polytetrafluorethylene (PTFE) porous film, or the like, is wound on a surface of the cylindrical molded product and RTV (room temperature vulcanization) silicone rubber is applied onto end and lap portions of the oil coating quantity control layer to adhesively bond the oil coating quantity control layer to the cylindrical molded product. There is also an oil coating roller in which the aforementioned oil coating quantity control layer is treated so as to be shaped like a tube and in which the oil coating quantity control layer is applied to cover a cylindrical oil holding member and heated so as to be shrunken (see JP-A-9-185282).
There is a further copying-machine coating mechanism in which an oil coating quantity control layer formed by crosslinking is provided on a surface of a thick porous tissue material as an oil holding member after a void tissue of porous polytetrafluorethylene is impregnated with a mixture of silicone rubber and release oil (see JP-B-6-73051). That is, the copying-machine coating mechanism is formed by: winding the oil coating quantity control layer by one turn as a roll on a surface of the thick porous tissue material; and then heating the oil coating quantity control layer at a high temperature for a long time to thereby perform crosslinking and thermally fusion-bond the oil coating quantity control layer to the surface of the thick porous tissue material. According to the copying-machine coating mechanism, silicone oil, which is release oil, can be controlled exactly and particularly silicone oil can be controlled stably in a long term even in a region in which a very small quantity of silicone oil is applied for oilless toner. Not only the roller shape but also a structure in which oil is applied onto the fixing roll by a flat-shaped pad is known as the form of the oil coating apparatus.
In the oil coating roller having the oil coating quantity control layer adhesively bonded to the cylindrical molded product, not only release oil is little put out from the adhesive portion so that unevenness occurs in the application of oil but also the adhesive area is so small that the oil coating quantity control layer is displaced or peeled because of shortage of adhesive strength. Accordingly, it is difficult to apply release oil onto the heat-fixing roll continuously stably. In the oil coating roller having the tube-like oil coating quantity control layer thermally shrunken, the thermal shrinking of the oil coating quantity control layer is apt to become so uneven that the pore size varies. Accordingly, it is difficult to apply release oil onto the heat-fixing roll continuously stably. Further, in the copying-machine coating mechanism, the oil coating quantity control layer must be heated at a high temperature for a long time so as to be thermally fusion-bonded to the thick porous tissue material. Accordingly, there is a tendency that this treatment takes too much labor. Also in the coater having the pad-like structure for applying oil to the fixing roll, the same problem as described above arises in the method for adhesively bonding the oil coating quantity control layer to the outermost surface layer of the pad-like structure. That is, also in this case, not only release oil is little put out from the adhesive portion so that unevenness occurs in the application of oil but also the adhesive area is so small that the oil coating quantity control layer is displaced or peeled because of shortage of adhesive strength. Accordingly, there arises a problem that the quantity of coating of oil becomes unstable.
In consideration of the problems described in the background art, an object of the present invention is to provide (1) an oil coating roller by which a proper quantity of oil can be applied continuously from the start of use even in the case where the oil is low-viscosity silicone oil, (2) an oil coating roller in which wasteful exudation of oil is suppressed during the stop of paper feeding so that there is no fear of excessive oil application just after the restart of paper feeding, and (3) an oil coating roller by which oil can be applied so extremely evenly that unevenness in the depth of toner does not occur in a fixed image even in the case where copying or printing is performed for OHP paper.
Another object of the present invention is to provide a method for adhesively bonding an oil coating quantity control layer toan oil holding member easily, and an oil coating apparatus using the method in which release oil can be applied onto a heat-fixing roll evenly as well as the oil coating quantity control layer is prevented from being displaced or peeled during the operation of the oil coating apparatus.
The oil coating roller according to the present invention is characterized as follows. The oil coating roller uses a porous round-rod-like molded product (inclusive of a hollow cylindrical molded product) as an oil holding member. Preferably, the porous round-rod-like molded product is made from heat-resistant fibers bound to one another by a binder and has fine communicating voids free from the binder among the fibers and evenly distributed pores with a pore size of from 0.05 to 2 mm and a total void percentage of from 30 to 90%. The porous round-rod-like molded product is impregnated with silicone oil. A heat-resistant fiber felt layer having a thickness of from 0.5 to 5 mm is provided on the outer circumference of the porous round-rod-like molded product. Preferably, an elastic body layer having communicating pores and having a thickness of from 0.3 to 3 mm and a compressive hardness of from 0.03 to 1.5 N/cm2 is provided on the outer circumference of the felt layer. The outer circumference of the elastic body layer is covered with a porous film having a thickness of from 15 to 130 xcexcm, a mean pore size of from 0.1 to 3.0 xcexcm (preferably from 0.1 to 1.0 xcexcm), a porosity of from 60 to 90% and an air permeability of from 3 to 2000 sec per 100 cc (preferably from 3 to 1500 sec per 100 cc) as the outermost surface layer.
With respect to the method for adhesively bonding an oil coating quantity control layer to an oil holding member easily, and the oil coating apparatus using the method, it has been found that silicone oil can be applied onto a heat-fixing roll evenly when an oil coating quantity control layer is adhesively bonded to the oil holding member by a mixture of an adhesive and silicone oil. Since the mixture is in a state in which the adhesive and silicone oil are dispersed in each other, portions in which pores of the oil coating quantity control layer are blocked by adhesion between the oil holding member and the oil coating quantity control layer on the basis of hardening of the adhesive are dispersively coexistent with portions in which the pores are not blocked by the interposition of unreacted silicone oil. Accordingly, the dispersed adhesive portions prevent the oil coating quantity control layer from being displaced or peeled, and the dispersed silicone oil portions serve as oil passages.
Furthermore, it has been found that the aforementioned effect concerning unevenness in application of oil can be obtained when a felt having a bending resistance (according to JIS L-1096) of from 30 to 90 mm (preferably from 50 to 70 mm) is used as the heat-resistant fiber felt without providing a two-layer structure of the felt.